The novel tells about the fate of five sisters living in Ireland at the end of the 19th century. The history of their family begins in France a thousand years ago, when Count Fulk the Red (a historical figure known as Count Fulk I of Anjou) married a girl whose fantastic embodiment was a unicorn, a mythical creature, but in this case described as real. As a result of this marriage, a succession of descendants emerged, usually of major historical figures, members of the royal families of France, England and other countries in Europe and around the world. Distant descendants of Fulk the Red and the unicorn are also the girls, the daughters of Sir John Green. Their family settled on the abandoned island of St. Alban, located on the Atlantic coast of Ireland; In this harsh environment, each girl lives her dreams, realizing her own destiny, different from the fate of her sisters. It was here that the main character of the novel, Sir Green's third daughter, Griselda, was born. For her, the ocean surrounding the island is a prison, and she lives in dreams of a liberator. Soon she meets an unusual young man named Shaun...